/Engine/Source/Runtime/Engine/Public/MaterialExpressionIO.h
const [UE::HLSLTree::FExpression](API\Runtime\Engine\HLSLTree\FExpression) * AcquireHLSLExpressionOrExternalInput ( [FMaterialHLSLGenerator](API\Runtime\Engine\FMaterialHLSLGenerator) & Generator, [UE::HLSLTree::FScope](API\Runtime\Engine\HLSLTree\FScope) & Scope, [UE::HLSLTree::Material::EExternalInput](API\Runtime\Engine\UE__HLSLTree__Material__EExterna-) Input, int32 InputIndex ) const